Baroreceptor reflex mechanisms will be studied in normal and age-matched hypertensive man. Carotid baroreceptors will be stimulated using a neck suction device; input parameters which will be varied include intensity, duration, and dp/dt. Outputs to be measured include pulse interval, A-H time, ventricular dp/dt, cardiac output and forearm vascular resistance. BIBLIOGRAPHIC REFERENCES: Abboud, F.M., Mark, A.L., Heistad, D.D., Eckberg, D.L., and Schmid, P.G.: Selectivity of Autonomic Control of the Peripheral Circulation in Man. Tr. Am. Clin. and Climatol. Assoc., 184-197, 1975.